The present invention relates generally to a method of suitably texturing/roughening at least part of the exposed surface(s) of articles comprising amorphous and/or fine-grained metallic materials to render their surface fluid-repellant, particularly water-repellant by introducing a dual surface structure.
Water repellant (hydrophobic), super-hydrophobic and self-cleaning surfaces are desired in numerous applications involving, at least at times, exposure to the atmosphere or water. As metallic surfaces are inherently hydrophilic (contact angle for water less than 90°), hydrophobic surfaces (contact angle for water greater than 90°), according to the prior art, are created by coating the surface of metallic articles with a suitable inherently hydrophobic material, e.g., organic coatings. Organic coatings, however, suffer from chemical degradation, low hardness, creep, poor wear and abrasion resistance and poor adhesion. Consequently, rendering metallic surfaces water repellent without requiring the application of soft polymeric hydrophobic coatings of poor durability is therefore highly desirable.
Fine-grained and/or amorphous metallic materials, layers and/or coatings that are strong, hard, tough and aesthetic can be produced in free standing form or can be applied to a variety of substrates as layers and/or coatings by a number of commercial processes including, but not limited to, electroless deposition, electrodeposition, cold spraying, rapid solidification and severe plastic deformation.
Various patents that address the fabrication of fine-grained and/or amorphous metallic coatings and articles for a variety of applications are known.
U.S. Pat. No. 3,303,111 discloses amorphous nickel phosphorus (Ni—P) and/or cobalt phosphorus (Co—P) coatings using electroless deposition.
U.S. Pat. No. 4,529,668 discloses an electrodeposition process for depositing boron-containing amorphous alloys having high hardness and wear resistance and sufficient ductility to avoid cracking of the amorphous layer in fabrication and use.
U.S. Pat. No. 5,389,226 discloses amorphous and microcrystalline electrodeposited nickel-tungsten (Ni—W) coatings of high hardness, wear and corrosion resistance and low residual stress to avoid cracking and lifting of the coating from the substrate.
U.S. Pat. No. 5,032,464 discloses smooth ductile alloys of a transition metal and phosphorus, particularly nickel phosphorus (Ni—P) with high ductility (up to 10%) produced by electrodeposition.
U.S. Pat. No. 5,288,344 describes beryllium (Be)-bearing alloys which form amorphous metallic glasses upon cooling below the glass transition temperature at a cooling rate appreciably less than 106 K/s.
U.S. Pat. No. 7,575,040 describes a process for continuous casting amorphous metal sheets by stabilizing the molten alloy at casting temperature, introducing the alloy onto a moving casting body, and quenching the molten alloy to solidify it.
U.S. Pat. No. 5,352,266 and U.S. Pat. No. 5,433,797, both having the same assignee as the present application, both describe a process for producing nanocrystalline materials, particularly nanocrystalline nickel. The nanocrystalline material is electrodeposited onto a cathode in an aqueous acidic electrolytic cell by application of a pulsed current. It is noted that the corrosion behavior of nanocrystalline nickel is different from polycrystalline nickel and suggested that, in the case of nanocrystalline nickel, uniform general corrosion is the dominant corrosion mechanism and neither pitting nor intergranular corrosion is observed.
U.S. Patent Publication No. 2005/0205425 and DE 10228323, both having the same assignee as the present application, disclose a process for forming coatings, layers or freestanding deposits of nanocrystalline metals, metal alloys or metal matrix composites. The process employs tank plating, drum plating or selective plating processes using aqueous electrolytes and optionally a non-stationary anode or cathode. Nanocrystalline metal matrix composites are disclosed as well.
U.S. Patent Publication No. 2009/0159451, which has a common assignee as the present application, discloses graded and/or layered, variable property electrodeposits of fine-grained and amorphous metallic materials, optionally containing solid particulates.
U.S. Ser. No. 12/548,750, which has a common assignee as the present application, discloses fine-gained and amorphous metallic materials comprising cobalt (Co) of high strength, ductility and fatigue resistance.
U.S. Ser. No. 12/785,662, which is a continuation-in part of U.S. Ser. No. 12/476,455, entitled “METAL CLAD POLYMER ARTICLE”, and is filed concurrently with the present application, discloses metal-clad polymer articles comprising polymeric materials having fine-grained (average grain-size being about 2 nm to about 5,000 nm) and/or amorphous metallic materials of enhanced pull-off strength between the metallic material and the polymer which are optionally wetproofed.
DE 10108893 describes the galvanic synthesis of fine-grained group II to group V metals, their alloys and their semiconductors compounds using ionic liquid or molten salt electrolytes.
U.S. Pat. No. 5,302,414 describes a cold gas-dynamic spraying method for applying a coating to an article by introducing metal or metal alloy powders, polymer powders or mixture thereof into a gas stream. The gas and particles, which form a supersonic jet having a velocity of about 300 to about 1,200 m/sec, are directed against a suitable substrate to provide a coating thereon.
U.S. Pat. No. 6,895,795 describes a method of processing a billet of metallic material in a continuous manner to produce severe plastic deformation. The billet is moved through a series of dies in one operation to produce a billet with a refined grain structure.
U.S. Pat. No. 5,620,537 describes a method of superplastic extrusion for fabricating complex-shaped, high strength metal alloy components by carefully controlling strain rate and temperature to retain an ultra-fine grained microstructure. A high strength, heat treatable metal alloy is first processed, such as by equal channel angular extrusion (ECAE), to have a uniform, equiaxed, ultra-fine grain size in thick section billet form.
U.S. Pat. No. 5,872,074 discloses leached nanocrystalline materials, specifically powders, having a high surface area for use as hydrogen storage material or as catalysts in the manufacture for fuel cell electrodes. The nanocrystalline material can be subjected to a leaching treatment in order to partially or totally eliminate one of the elements of the composite or alloy resulting in a porous structure and a high specific surface area.
The prior art also describes various means of increasing the water repellent properties of hydrophobic, predominantly polymeric surfaces by roughening.
U.S. Pat. No. 3,354,022 describes water repellent surfaces having an intrinsic advancing water contact angle of more than 90° and an intrinsic receding water contact angle of at least 75° by creating a micro rough structure with elevations and depressions in a hydrophobic material. The high and low portions have an average distance of not more than 1,000 microns. The average height of high portions is at least 0.5 times the average distance between them. The air content is at least 60% and, in particular, fluorine containing polymers are disclosed as the hydrophobic material. The water repellent surfaces are created by using an embossing die made of hollow polymer fibers. Unfortunately, such coatings have a disadvantageously low abrasion resistance and only a moderate self-cleaning effect.
U.S. Pat. No. 6,660,363 describes self-cleaning surfaces of objects made of hydrophobic polymers or permanently hydrophobized materials which have an artificial surface structure of elevations and depressions wherein the distances between the elevations are in the range of from 5 to 200 μm, and the heights of the elevations are in the range of from 5 to 100 μm. The elevations consist of hydrophobic polymers or permanently hydrophobized materials and the elevations cannot be wetted by water or by water containing detergents. This is accomplished by attaching PTFE particles (7 micron in diameter) to a polymer adhesive film containing surface and curing the structure or by using a fine mesh screen to emboss a polymer surface by hot pressing. According to the '363 patent, such surfaces are produced by application of a dispersion of powder particles of an inert material in a siloxane solution, and subsequent curing the siloxane solution to form a polysiloxane. Unfortunately, the structure forming particles do not adhere well to the surface of the substrate in an abrasion stable manner and thus the abrasion resistance is undesirably low.
U.S. Patent Publication No. 2003/0187170 discloses a process for producing nanostructured and microstructured polymer films by guiding the polymer through a gap formed by a suitably patterned roll, and a means which develops an opposing pressure so that the polymer film is deformed and shaped in accordance with a relief pattern. The relief pattern on the form tool is created by sandblasting, etching, laser ablation, lithographic techniques, offset printing, electroplating techniques, LIGA and/or erosion.
U.S. Pat. No. 6,764,745 describes a structural member in which high water-repellency can be obtained by forming appropriate irregularities on the external surface. The irregularities comprise protrusion portions of uniform height and shaped as prisms and which are subsequently coated with a water repellent film of PTFE or fluoroalkylsilane. The surface features termed “irregularities” are dimensioned such that a water droplet cannot fall into the air-filled recesses.
U.S. Pat. No. 6,872,441 describes glass, ceramic and metal substrates with at least one self-cleaning surface comprising a layer with a micro-rough surface structure which is arranged on the substrate and made at least partly hydrophobic. The layer contains a glass flux and structure-forming particles with a mean particle diameter within the 0.1 to 50 micron range. The micro-rough surface, structure has a ratio of mean profile height to mean distance between adjacent profile tips between 0.3 and 10. The surface layer is produced by coating the substrate with a composition containing a glass flux and structure-forming particles, and the layer is burnt in and made hydrophobic.
Thus prior art teaches that, in order to raise the contact angle for water by adding surface features to a material, the material inherently has to be non-wetting/hydrophobic. According to the prior art teachings, structurally modified but inherently wetting surfaces, such as metallic surfaces, would simply fill with water expelling the air and accordingly remain wetting/hydrophilic.